1. Field of the Invention
This invention relates to display systems, more particularly to display systems using coherent light sources.
2. Background of the Invention
Laser illumination in displays has many advantages of standard lighting schemes, especially in color displays. Lasers produce high power light with good color purity. The mixture of red, green, and blue, laser light can be achieved relatively simply by standard optical components, including fold mirrors. Unfortunately, the use of one laser causes an interference problem, and that problem is compounded with the use of more than one laser.
Because each laser is coherent, having a continuous relationship between phases, when lasers are diffused using beam splitters and lens systems, the phase pattern results in a particular pattern of interference called speckle. A speckled picture cannot be viewed very clearly, if at all, since the interference patterns often cancel each other, resulting in a noisy, blurry picture. Putting three lasers together increases this problem to the point that the noise almost completely eliminates the desired picture.
Lasers are desirable for use with spatial light modulators, which normally have relatively small active areas, because of the increased illumination power. Many attempts have been made to overcome the speckle problem such as vibrating screens, acoustic waves, and very complex optical schemes of many components. These ideas result in very high costs, or extremely complex systems. Therefore, there exists a need for a low cost, simple solution that eliminates laser speckle in displays.